A model for the structure of fructose-1,6-bisphosphatase from pig kidney.

Fructose-1,6-bisphosphatase (EC. 3.1.3.11) is an allosteric enzyme that plays a key role in the gluconeogenesis process. It forms a tetramer of identical subunits, its action is inhibited by AMP, it requires the presence of a divalent cation to be active and it is proteolytically regulated. The prediction of the secondary structure of this enzyme was done by the hydrophobicity profiles' method and by the Chou and Fasman's method with modifications. The predicted structure shows 38% beta-structure, 22% helical structure and 4% beta-turns. The structure can be described in terms of two domains joined by a 17-residues strand of random coiled structure. The location of the active and of the regulatory sites in the model proposed was made by secondary structure analogy with the enzyme obtained from rabbit liver. Domain I contains the AMP binding site and the proteolytic regulation site. Domain II has the active site, which, by appropriate superposition of both domains, can be located close to the AMP binding site and to the hyperreactive SH group. The model proposed meets several structural restrictions, it is thermodynamically stable and can explain the enzymatic behavior of the protein.